This invention relates to the removing of carbon dioxide from the air in general, and more particularly for an apparatus and method for carrying out such removal, which apparatus and method is particularly useful in removing carbon dioxide from the air used in operating metal-air batteries.
Because of the exhaust emissions of hydrocarbon fuels and also because of their recent shortage, there has been a great deal of interest in electric propulsion for motor vehicles. One of the primary problems associated with such propulsion is in the provision of suitable batteries. One type of battery suggested for such a use which type appears to be quite promising, is a metal-air battery. Because these batteries are operated using an alkaline electrolyte, it is necessary to remove the carbon dioxide from the air used before it is supplied to the air electrodes. Otherwise, the electrolytic liquid would become carbonatized. This, in turn, would result in the impairment or destruction of the metal and air electrodes. Similar problems occur in connection with other types of electrochemical cells which are operated with air such as fuel cells.
Various methods and apparatus have been developed for removing carbon dioxide from the air. In one of these, the air is washed with an alkaline solution in tanks filled with what are referred to as Raschig rings. For the elimination of small amounts of CO.sub.2, gel absorbers have also been used. Although these methods are efficient in removing carbon dioxide, they have a serious disadvantage in that the air must be at a fairly high pressure, because relatively high pressure losses occur during the washing process. Furthermore, in order to obtain the increased pressure, compressing means of some nature are required and these means use up a certain amount of energy. This additional energy used in compressing the air can have a particularly unfavorable effect with regard to electro-traction since the energy required for increasing the air pressure would have to be taken from the electrochemical current source being used and this energy would be lost to the main purpose, i.e., the electric propulsion.
Thus, it can be seen that there is a need for an improved method and apparatus for removing carbon dioxide from the air so that the resulting product may be used in the operation of electrochemical cells, which method and apparatus requires only a small increase of air pressure and an accordingly small amount of energy for operation.